An apple a day may indeed keep the doctor away, as long as you eat the peel. New research from the University of Iowa has shown that a waxy substance in apple peel, called ursolic acid, can reduce obesity, pre-diabetes and fatty liver disease in mice.

In the mouse study, researchers found that ursolic acid increased muscle and brown fat - a type of fat usually abundant in newborns that helps retain body heat by burning calories.

"From previous work, we knew that ursolic acid increases muscle mass and strength in healthy mice, which is important because it might suggest a potential therapy for muscle wasting," study lead Christopher Adams said. "In this study, we tested ursolic acid in mice on a high-fat diet -- a mouse model of obesity and metabolic syndrome. Once again, ursolic acid increased skeletal muscle. Interestingly, it also reduced obesity, pre-diabetes and fatty liver disease.

Like Us on Facebook

Over several weeks, Adams and his team studied mice likely to develop obesity and metabolic syndrome. They put the mice on a high-fat diet, with half of the animals receiving ursolic acid with their food. The mice given ursolic acid actually ate more than those not getting the supplement, and both groups had the same amount of activity. Still, the mice eating ursolic acid gained less weight and their blood sugar levels remained normal.

The supplement boosted the animals' skeletal muscle, increasing their strength and endurance, and resulted in higher levels of brown fat.

"Since muscle is very good at burning calories, the increased muscle in ursolic acid-treated mice may be sufficient to explain how ursolic acid reduces obesity. However, we were surprised to find that ursolic acid also increased brown fat, a fantastic calorie burner. This increase in brown fat may also help protect against obesity."

Brown fat was thought to exist only in infants and then disappear during childhood, until recently. Improved imaging techniques have shown that adults retain a small amount of the lipid mostly in the neck and between the shoulder blades.

"Brown fat is beneficial and people are trying to figure out ways to increase it," said Adams, according to My Health News Daily. "Our next step is to determine if ursolic acid can help patients."

Ursolic acid can also be found in cranberries, prunes, lavender, basil, oregano, rosemary and thyme. The Daily Mail reports that Adams now wants to work out if apple peel is as good for people as it is for mice, which would allow him to work out how many apples we'd need to eat to make muscles bulge and waistlines shrink.